The present invention relates generally to ships having a pair of submerged hulls supporting a platform above the water surface. These vessels are generally known as semi-submerged ships.
Most conventional surface vessels are subject to large pitching, heaving and rolling motions in heavy seas, both at rest and underway. Such large motions result in seasickness and discomfort, limit vessel speed, limit shipboard operations and vessel uses due to lack of stability on board, and produce large forces on the vessel structures.
In attempting to reduce wave motions, various ships have been designed in which the bulk of the vessel is lifted out of the water, for example, hydrofoil and air cushion supported vessels. Another type of vessel utilizes two submerged buoyant hulls to support a superstructure above the water line. One semi-submerged ship of this general type is described in my U.S. Pat. No. 3,623,444, in which two or more surface piercing struts support a platform above the water from two fin-stabilized submerged hulls. This construction greatly reduces motion in waves.
Other semi-submerged ship constructions are described in my U.S. Pat. Nos. 3,897,744; 3,866,557; and 3,842,772. U.S. Pat. No. 3,842,772 describes a bow impact alleviator to alleviate wave impacts on the cross-structure. This generally comprises projections on the underside of the cross-structure or platform, which are located at or near the bow of the vessel. In U.S. Pat. No. 3,866,557, the vessel comprises twin upper hulls and twin lower, submerged hulls attached together by means of four surface-piercing struts, with a cross-structure connecting the upper hulls. The surface-piercing struts are streamlined from front to rear. This construction is particularly suitable for small sailing boats. My U.S. Pat. No. 4,440,103 describes a semi-submerged ship having a superstructure supported on struts above a pair of submerged buoyant hulls, with cargo space in the struts and submerged hulls. Various shapes of connecting struts are described, including straight and tapered struts and struts having a tapered upper portion and a straight lower portion.
U.S. Pat. No. 4,174,671 of Seidl describes a semi-submerged ship in which the platform is joined to a pair of submerged hulls via struts which are tapered. British Pat. No. 1,260,831 of Shillito describes a vessel with a pair of composite hulls consisting of a floating upper part and a submerged lower part connected together by one continuous strut or two or more separate struts. The floating upper parts are connected by a cross-structure, and are of V-shape.
All of these various designs reduce wave motions over conventional surface boats. However, when travelling at speed in very heavy seas, some bow impacts can still occur, potentially causing damage to the structure. Generally, any means for reducing such impacts will create a much heavier structure with resultant payload penalties.